(URI) Apagando e Ganhando - Solution

Link to the problem: https://www.urionlinejudge.com.br/judge/pt/problems/view/1084

For this problem, it is necessary to use a stack, which will enable us to discard and keep the numbers.


import java.io.*;
import java.util.*;

class Main  {
    public static int reader(BufferedReader br) throws NumberFormatException, IOException {     
        int n;
        int resp = 0;     
      
        while (true) {         
            n = br.read();         
            if (n >= '0' && n <= '9') {
                break;
            }
        }
           
        while (true) {         
            resp = resp*10 + n-'0';         
            n = br.read();         
            if (n < '0' || n > '9') {
                break;     
            }
        }
      
        return resp;     
    }
   
    public static void process() throws NumberFormatException, IOException {  
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
       
        int numDigits = reader(br);
        int numDigitsErase = reader(br);
        while (numDigits != 0 || numDigitsErase != 0) {
            String number = br.readLine();
           
            int countDigitsErased = 0;
            Deque<Integer> stack = new ArrayDeque<Integer>();
            for (int i = 0; i < numDigits; i++) {
                int digit = number.charAt(i)-'0';
                while (stack.size() > 0 && digit > stack.peekFirst() && countDigitsErased < numDigitsErase) {
                    stack.pollFirst();
                    countDigitsErased++;
                }
                stack.addFirst(digit);
            }
            for (int i = countDigitsErased; i < numDigitsErase; i++) {
                stack.pollFirst();
            }
           
            while (stack.size() > 0) {
                System.out.print(stack.pollLast());
            }
            System.out.println();
           
            numDigits = reader(br);
            numDigitsErase = reader(br);
        }
                                               
        return;
    }
  
    public static void main(String[] args) throws NumberFormatException, IOException {
        Main m = new Main();
        m.process();

        System.exit(0);
    }
}